1. Field of the Invention
The present invention generally relates to work platform lift machines and, more particularly, is concerned with a scissors-type work platform lift machine with an electro-mechanical based lift actuation arrangement.
2. Description of the Prior Art
In various work platform lift machines, such as scissors lifts, elevated platforms, cranes, etc., hydraulic cylinders are used to provide the necessary lifting forces. One of most popular machines of this type in use is called an electric slab scissor lift machine. Electric slab scissor lift machines commercially available at present time from several manufacturers include a battery powered chassis having rear stationary wheels and front steerable wheels, a scissors lift mechanism mounted at a lower end on the chassis, a work platform mounted on an upper end of the lift mechanism for carrying workmen, and a hydraulic actuation system for operating the lift mechanism to raise and lower the work platform. The scissors lift mechanism includes a plurality of sets of arms pivotally interconnected in a scissor-like fashion so as to raise and lower as the arms pivot between generally vertical unstacked and horizontal stacked orientations relative to one another. The hydraulic actuation system generally employs one or more hydraulic cylinders for causing pivoting of the sets of arms to expand the lift mechanism by unstacking the sets of arms and thereby raise the work platform or to retract the lift mechanism by restacking the pairs of arms and thereby lower the work platform. Typically, the hydraulic cylinders are interconnected between an adjacent set of the arms.
The use of hydraulic actuation systems and positioning of the hydraulic cylinders in lift machines have several disadvantages. One major disadvantage is that hydraulic actuation systems leak hydraulic fluid which is a substance toxic to the environment and therefore requires a considerable amount of care and attention and must be contained and disposed of properly. In food, aerospace, pharmaceutical, silicon chip and other industries, cleanliness is very important and thus hydraulic fluid leakage and contamination cannot be tolerated. Another significant disadvantage of hydraulic actuation systems is that they are not very efficient, typically operating at levels ranging from fifty to sixty percent efficiency. Thus, lift machines that are hydraulically powered not only invite high maintenance and/or repair costs but also tend to tax the batteries that are used to drive the machines resulting in short run times before the batteries need to be recharged. Yet another important disadvantage is that using hydraulic cylinders within the scissors arm stack to raise the lift mechanism and thereby the work platform not only causes machine instability due to high centers of gravity, but also such hydraulic cylinders tend to be squishy and jerky in operation and thus hydraulic actuation systems lack smooth and precise control of the movement of the lift mechanism to raise and lower the working platform.
Consequently, a need exists for a different approach to actuation of the scissors lift mechanism of such lift machines which will overcome the above-mentioned disadvantages without introducing other disadvantages in their place.